High Frequency Direction Finding
HFDF
9/8/2014
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On Target Enterprises Overview
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Woman-Owned Small Business
Cocoa Florida Main Office
Receiver development laboratory
System test ranges
– 500 acre open field range in Colorado
– 15 acre jungle range in Florida
• Products
– MISER: UHF/VHF detect/DF/record
– WATCHDOG: HF detect/DF/map/record
– SentryGo: Marine Navigational Radar detect/DF/characterize
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Direction Finding
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What is Direction?
Azimuth and or Elevation
Polarization
Time (or time difference)
Frequency (or frequency
difference)
• Vector Space
– Complex difference of signals
between antennas
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Applications of HF Direction Finding
• Finding sources of interference to
communications
• Locating transmitters
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Hostile forces
Amateur radio contest beacons
Distress signals
FCC or ITU violations
Understanding the ionosphere
Deep space mapping
Maximizing receive/transmit link quality
SETI
LOFAR Array
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Classic Challenges to HF DF
• High interference
• Long wavelength (large footprint)
• Propagation variance
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Atmosphere and Ionosphere
Time delay, Doppler
Polarization rotation, birefringence
Aggregate propagation paths
• Multipath
• Wide fractional bandwidth
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Tactical HF DF Challenges
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“Tactical” systems need to be
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Light weight, low power
Economical
Rugged, repairable
Quick to deploy, easy to use
HF DF systems must exhibit
– Sensitivity to weak signals (requiring large antennas)
– Large dynamic range (requiring significant power)
Conflicting
Requirements
• In the presence of high interference across large bandwidth
– Channel measurement accuracy (to determine “direction”)
• Requiring large separation between antennas
– Some method of calibration
• To angle and polarization
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Technologies Applicable to Modern HF DF
• Active Antennas
– Small, E or H field, no mutual impedance
• Fast Analog to Digital Converters (ADC)
– Low power, high precision
• High speed data acquisition, transfer, storage
– USB, Ethernet,
• Fast Digital Signal Processing (DSP)
– Special purpose hardware, software, FPGAs
• Widely distributed time synchronization
• Wide area/bandwidth networking
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The HFDF Process
Design receiver network
Tactical Readjustment
H2
Deploy
V1
Task receivers
V2
H1
Detect
H0
Measure complex response across channels
V3
H3
Interpret against antenna calibration
Model ionosphere
Display results on map
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On Target Enterprises
Services
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System analysis
Conceptual design
Proof of concept
Critical element demonstration
Products
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9/8/2014
Tactical radio detection and DF
HF, UHF/VHF, microwave
Small, lightweight, modular, rugged
Low cost per unit
Broadband access
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Wideband continuously
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Narrowband precision tasking
Power solutions; battery, solar, shore
Real-time monitoring and recent activity
logging
Integrated processing and laptop GUIs
Field level
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Array configuration
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Software module interaction
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Networking
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Troubleshooting, repair
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HF System Modules
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N-Wideband channels (50 MHz)
– Coherent, time-synchronized, snapshot processing
– 1 to 3 KHz frequency resolution
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M-Narrowband channels (11kHz to 200 kHz)
– Slaved to wideband system
– Coherent, time-synchronized, continuous processing
– Arbitrary frequency resolution
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Worldwide tactical mapping
– Array planning, site selection, accuracy prediction
– Real time tactical display
– Playback with customized processing of multichannel narrowband
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TDOA/FDOA narrowband time-tagging
– Correlation processing
– Self calibration, maintenance, and ionospheric monitoring from ionosondes
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Polydimensional analyzer (PolyAna)
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Possible Deployment
Active V-pol
Antenna Element
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Polarization and array spacing driven by
frequency range of interest
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Deployed, calibrated by two people in 1
hour
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Small SUV transportable
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24/7 operation with solar/batteries
Active H-pol
inverted-vee
turnstyle element
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Possible Operating Modes
Frequency dependent threshold
Composite Spectrum showing rich signal density
Real-time full HF spectrum monitoring
- DF all signals simultaneously
- Adjustable threshold vs frequency
- Detections, DFs, etc. stored
- Self triggered narrow band analysis
Falling raster display
Multi-day environment analysis
- Display every signal hit with DF
- More than two weeks of data storage
- Narrowband analysis overlays
Date
and
Time
Radio Frequency
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Possible Operating Modes
Multiple sites commanded into narrowband beamforming mode
- Simultaneous time-coherent collection scheduled
- Correlation processing applied to map energy density
- Low cost massive aperture deep space array
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System Performance and Accuracy
Performance measure
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Sensitivity
Amplitude, phase accuracy
Wavefront angle accuracy
Incident polarization
Solution delay
Transmitter location solution
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Limiting Aspects
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Noise
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Interference
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Signal Characteristics
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Frequency, bandwidth
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Transmitting power
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Up-time
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A-priori knowledge
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Movement
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Selection of array elements and geometry
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Ionosphere characteristics and model
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Real-time updates
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Processing power
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O vs. X propagation modes
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Inter-system network bandwidth
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Number of systems deployed
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Ability to relocate receivers
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Observables measured and processed
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System calibration
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Mapping Interface
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Thank You
• John Hoover
– john@ontargetenterprises.com
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